Scientists have said that some people can halt and even reverse the ageing process in their thirties.

The study focused on 954 people in the New Zealand city of Dunedin who have been tracked for several years.

The researchers devised a measure called ‘biological age’ to assess how worn out the participants’ bodies were internally.

Duke researchers analysed medical data from almost a thousand 38 year olds. While some appeared medically in their late 20s, some seemed almost 60.

They had biologically aged zero years, and had even begun to look younger while others were found to have aged biologically by three years for each calendar year.

Thus the research team which cut across universities in Britain, the US, Israel and New Zealand said such people may hold the key to developing what would in effect be a fountain of youth.

Health measures like blood pressure and liver function were taken regularly, along with interviews and other assessments.

It was reported that the progress of aging shows in human organs just as it does in eyes, joints and hair, but sooner.

So as part of their regular reassessment of the study population at age 38 in 2011, the team measured the functions of kidneys, liver, lungs, metabolic and immune systems.

They also measured ’good’ cholesterol, cardiorespiratory fitness, lung function and the length of the telomeres, protective caps at the end of chromosomes that have been found to shorten with age.

Using their assessment, they found some of the 38-year-olds had a body age more like 60. A few were up to eight years ‘younger’ than their real age, and three had not ‘aged’ at all over the tested period.

Further tests revealed that those who seemed older on the inside also appeared older to others who were asked to guess their age.

Also, those who were more advanced in biological ageing also scored worse on balance and co-ordination tests usually given to over-60s, and had more difficulty with activities such as walking upstairs.

The researchers say the ultimate goal is to be able to intervene in the ageing process itself, rather than addressing killers such as heart disease or cancer in isolation.

Speaking on the study, Prof. Terrie Moffitt, also of Duke University and King’s College, London said smoking and serious mental illness can speed up the ageing process, while intelligence seems to keep the body young.

The researchers also said genes play a role in the aging process and pinning this down could lead to new anti-ageing drugs.